A Study to Evaluate the 24 Hour Spirometric Effect (FEV1) of Fluticasone Furoate/Vilanterol Inhalation Powder (100mcg Fluticasone Furoate (FF)/25mcg Vilanterol (VI)) Compared With Salmeterol/Fluticasone Propionate Inhalation Powder (50mcg Salmeterol/500mcg Fluticasone Propionate (FP))

This is a randomized, double-blind, double-dummy, multi-centre parallel group study. Subjects who meet the eligilibilty criteria at Screening and meet the randomization criteria at the end of a 2-week Run-In period will enter a 12-week Treatment period. There will be a 7-day Follow-up period after the treatment period.